My 83 300SD has 180,000 miles and I do not have a record of the chain being replaced. I've been trying to wrap my head around the whole timing chain/offset keys system. I assume that the offset keys are to compensate for the slight differences in machining and resulting differences in cam timing even with a new chain. I imagine that usually an offset key needs to be used to set the cam precisely. I recently adjusted the pump timing which was retarded by 8° at the crank. I got concerned about the timing chain. I then looked into how to check the timing chain stretch and did so. The cam was retarded by
1 1/2-2°. At the time I thought that was fine as 5° is the point I have heard to replace the chain. Then I got to thinking about the possibility that someone had already compensated for chain stretch by using an offset key. Is there any way to tell?

Andrew